In recent years, photon-counting type X-ray CT apparatuses of performing photon counting computed tomography (CT) by using a photon-counting type detector have been developed. Unlike an integration type detector used for an X-ray CT apparatus of the related art, the photon-counting type detector outputs a signal capable of individually counting X-ray photons transmitting through a test object. Therefore, in the photon counting CT, an X-ray CT image having a high signal to noise (SN) ratio can be reconstructed.
In the above-described photon counting CT, as the detector, a direct-conversion type semiconductor detector made of cadmium telluride (CdTe), cadmium zinc telluride (CdZnTe), or the like, an indirect-conversion type detector such as scintillator, or the like is used. Since the signal of such a detector is weak, in general, integrated circuitry such as an application specific integrated circuit (ASIC) is arranged in the vicinity of the detector.
In the ASIC used as a detector in photon counting CT, for example, a pre-amplifier is arranged at the first stage to perform signal amplification, and at the subsequent stage, a waveform of the signal is shaped, so that incident X-ray photons are discriminated into a plurality of energy bands according to energy of the photons. Accordingly, in the photon counting CT, images of the plurality of the energy bands can be simultaneously acquired, and a reconstructed image of a plurality of substances can be acquired.